Multileaf collimator: Difference between revisions

Revision as of 20:56, 5 March 2007

Revision as of 05:46, 22 March 2007

Line 1:

A '''multileaf collimator''' (also known as an '''MLC''') is device used inon [[radiotherapy]]linear foraccelerators definingto theprovide shapeconformal shaping of aradiotherapy treatment fieldbeams. Specifically conformal radiotherapy and Intensity Modulated Radiation Therapy (IMRT) can be delivered using MLC’s.

[[Image:NeutronPort.gif|thumb|right|Simulation of a treatment neutron field collimated using MLC. The white bars represent MLC leaves]]

The goal of [[external beam radiotherapy]] is to deliver a target [[radiation dose|dose]] to the [[tumour]] while sparing dose to healthy tissue as much as possible. In order to achieve this goal, the radiation beam must be shaped to match the shape of the tumor from the [[beam's eye view]]. As it takes about 10cm of lead or tungsten to block radiation, this shaping is not easy to do automatically. The multileaf collimator was designed to do precisely that. A standard MLC consists of 40 or more pairs of tungsten plates called "leaves". Each leaf can move independently in towards in centre of the treatment field, creating an approximation of any desired shape.

The MLC has improved rapidly since its inception and the first use of leaves to shape structures in 1965 (Takahashi 1965) to modern day operation and use. MLC’s are now widely used and have become an integral part of any radiotherapy department. MLC’s were primarily used for conformal radiotherapy, and have allowed the cost effective implementation of conformal treatment with significant time saving (Brewster et al 1995, Helyer and Heisig 1995), and also have been adapted for use for IMRT treatments. For conformal radiotherapy the MLC allows conformal shaping of the linear accelerator (LINAC) beam to match the borders of the target tumour. For intensity modulated treatments the leaves of a MLC can be moved across the field to create IMRT distributions (it should be noted here that MLC’s really provide a fluence modulation rather than intensity modulation).

The MLC is an important tool for radiation therapy dose delivery. It was originally used as a surrogate for alloy block field shaping and is now widely used for IMRT. As with any tool used in radiotherapy the MLC must undergo commissioning and quality assurance. Additional commissioning measurements are completed to model a MLC for treatment planning. Various MLC’s are provided by different vendors and they all have unique design features as determined by specifications of design (Galvin 1993), and these differences are quite significant.

The MLC was later discovered to be ideal for [[intensity-modulated radiotherapy]] (IMRT). IMRT involves optimising the precise amount of radiation that should be applied to each part of the beam in order to deliver an ideal treatment. By layering multiple MLC deliveries with different shapes atop one another, an approximation of this ideal treatment can be achieved.

[[Category:Radiobiology]]

{{med-stub}}